This invention relates to the use of a conductive polymer material to selectively control light transmission through a transparent or semitransparent panel or film, and more particularly to the use of a conductive polymer material to provide a window shade of adjustable transmittance. Such a device may be embodied as a flexible adhesive-backed laminated plastic sheet, or as an integral part of a multiple-pane thermal insulating window panel.
Thermal-pane windows conventionally make use of spaced multiple (two or more) panes to provide a thermal barrier restricting heat conduction between the outside and the inside of a building and therefore tending to reduce heating and cooling costs. To further reduce cooling costs, window shades or blinds are used to block out intense, direct rays of sunlight, since conventional windows, insulating or otherwise, have little effect on radiative heating. However, in using a conventional shade to eliminate solar glare, the view to the outside is blocked, which may be considered a visually unattractive result. U.S. Pat. No. 4,268,126 discloses a multi-pane window unit that uses an electrooptical shade as an integral part of a thermal pane window. Such a device relys on diffuse reflection of light rays to provide mainly privacy. The effectiveness of such a window to control radiative heating (solar energy) is limited by the ability of the window device to reduce transmitted radiation by mainly diffuse scattering and not by optical absorption. Devices listed in U.S. Pat. No. 4,268,126 typically reduce solar radiative heating by up to 15%.
Thus, there exists a need for a window unit which includes an electrooptical device as an integral part of a thermopane window that provides a broad adjustable range of coherent light transmittance in both the visible and near-IR region of the electromagnetic spectrum. Such a window device which relies on absorption rather than diffuse reflectance can be used to control glare and the degree of radiative heating from sun rays while not blocking or obscuring the view from the outside.
The present invention makes use of conductive polymer material to provide adjustable control of the intensity of light transmission through a multi-pane thermal window unit or in automobile or aircraft windows or mirrors where adjustable light transmission is desired. The room occupant may select the degree of light transmittance of the shade, thus eliminating glare and the adverse effect on cooling requirements from direct rays of the sun, while not blocking the view to the outside.
Conjugated backbone polymers, e.g., polyacetylene, polyphenylene, polyacenes, polythiophene, poly(phenylene vinylene), poly(thienylene vinylene), poly(furylene vinylene), polyazulene, poly(phenylene sulfide), poly(phenylene oxide), polythianthrene, poly(isothianaphthene), poly(phenylquinoline), polyaniline, and polypyrrole, and the like have been suggested for use in a variety of electronic applications based upon their characteristic of becoming conductive when oxidized or reduced either chemically or electrochemically. Electrodes composed of such polymers can, according to the method of MacDiarmid et al. in U.S. Pat. No. 4,321,114, be reversibly electrochemically reduced to an n-type conductive state (the polymer being inserted by cations) or reversibly oxidized to a p-type conductive state (the polymer being inserted by anions).
The electrochemical oxidation or reduction process is generally recognized to be accompanied by sharp changes in the color of the polymer as well as its optical absorption coefficient (its ability to transmit light). Electrochromic devices based on conductive polymers have been described for example by F. Garnier et al. in J. Electroanal. Chem. 148, 299 (1983), by K. Kaneto et al. Japan J. Appl. Phys 22, L412 (1983), and by T. Kobayashi et al., J. Electroanal. Chem. 161, 419 (1984).